Light source for shadow mask tubes



April 30, 1968 D. THORNTON LIGHT SOURCE FOR SHADOW MASK TUBES 4 Sheets-Sheet 1 Filed Dec. 10, 1965 INVENTOR.

0006!..7 mum/raw April 30, 1968 D. THORNTON 3,380,354

LIGHT SOURCE FOR SHADOW MASK TUBES Filed Dec. 10, 1965 4 Sheets-Sheet E5. E

April 30, 1968 D. THORNTON 3,380,354

LIGHT SOURCE FOR SHADOW MASK TUBES Filed Dec. 10, 1965 I 4 Sheets-Sheet 5 iii 5-317..

D. THORNTON LIGHT SOURCE FOR SHADOW MASK TUBES A ril 30, 1968 4 Sheets-Sheet 4 Filed Dec. 10, 1965 FL llllll INVENTOR. Magyar Mae/v2? United States Patent 3,380,354 LEGHT SOUEMJE FOR SHADOW MASK TUBES Douglas Thornton, Chicago, Ill., assignor to National Video (Zorporation, Chicago, llh, a corporation of Illinois Filed Dec. 10, 1965, Ser. No. 513,033 9 Claims. (Cl. 95-1) ABSTRACT OF THE DKSCLOSURE pattern.

The instant invention relates to color television and more particularly to a novel light source employed in a lighthouse apparatus used to form phosphor dot patterns in color tubes of the shadow-mask variety.

Shadow mask tubes are well known in the color television receiver art and are typically comprised of at least one electron beam source and a multi-apertured shadow mask which is positioned adjacent the tube face. Deflection means are provided to deflect the electron beam, horizontally and vertically to trace out a raster. The tube face is provided with a plurality of phosphor dots of each of the three primary colors. The geometry of the electron beam, shadow mask and phosphor dot pattern is so arranged as to cause each of the electron beams to strike phosphor dots of only one associated primary color to the exclusion of the remaining colors.

The phosphor dot pattern is conventionally formed upon the face of the tube by forming a slurry containing phosphor material of one primary color, a photosensitive binder and an adhesive material; uniformly applying the slurry upon the tube face; and passing light rays through the multi apertured shadow mask. The exposed portions of slurry harden and adhere tightly to the glass surface due to the presence of the photosensitive binder. The tube face then undergoes a washing process which removes the unexposed portions of slurry. The exposed portions remaining are substantially in the form of dots due to the circular-shaped apertures in the shadow-mask which the light rays pass through.

The above steps are repeated for each of the three primary colors so as to develop a phosphor dot pattern with the phosphor dots of the 3 primary colors forming a large number of triads upon the tube face.

In the light exposure phase of the process, it is conventional to employ a light source, for example, a mercury arc lamp, which has its light rays directed upon a tapered transparent member, such as, for example, a quartz member so as to simulate a point light source. The radiation pattern for such light source is substantially circular, and hence, the intensity of the light greatly diminishes for rays in the vicinity of the edges of the tube face. It is, therefore, extremely important to provide a light source which has a superior radiation pattern so that the light rays impinging upon the tube face in the region of the edges of the tube face will have an intensity which is greater than the intensity of light rays directed toward central region of the tube face. This requirement is a result of the shadow mask apertures which are smaller in diameter in the region of the edges.

The instant invention is comprised of a high intensity light source which is located within a substantially closed housing. The lower half of the housing is a substantially dome-shaped highly-polished reflective surface, arranged to reflect light rays so that substantially all of the light rays will be directed toward the region of an opening provided toward the upper end of the housing.

The reflector portion has a substantially ellipticalshaped surface, which configuration is chosen as to appropriately deflect the light rays toward the opening provided at the upper end of the housing.

A lens is mounted within the housing opening and has a configuration and index of refraction so as to deflect the light rays impinging upon the lens to pass through the lens and the housing opening so as to form a radiation pattern having a configuration of a cardioid (i.e. heartshaped). In addition, where the light source is an ideal point light source, the objective of the lens is to deflect light rays, which should all impinge upon a single focal point within the lens, to an angle of no greater than 45 relative to the color tube longitudinal axis. As a practical matter the lamp structures presently available deviate somewhat from the ideal point light source condition. Hence the design of the instant invention was chosen to cause the light rays to fall upon a locus curve contained within the design of the lens such as to deflect the maximum number of light rays by no more than a 45 angle from the longitudinal axis for illuminating the tube face so as to obtain an extremely enhanced radiation and to fully compensate for imperfections in the light source.

Additional approaches to this problem have consisted of providing a filter or other similar member positioned between the mercury arc source and the tube face of the color tube being illuminated, wherein the member is coated with some material so as to attenuate the light rays directed toward the center of the tube face and to allow the light rays in the regions of the edges of the tube face to be substantially unattenuated. This approach, of necessity, significantly diminishes the intensity of illumination. In the instant invention, the lens in no way attenuates the light ray intensity but simply redistributes the radiation pattern in such a fashion as to provide light rays of much greater intensity in the region of the edges of the tube face than the pattern obtained through the use of conventional approaches.

It is therefore one object of the instant invention to provide a novel light source.

Another object of the instant invention is to provide a novel light source for use in a lighthouse structure employed to form phosphor dot patterns upon tube faces of shadow-mask color tubes.

Another object of the instant invention is to provide a light source for use in lighthouse structures and the like wherein the light rays emanating from the lighthouse have a cardioidic intensity pattern.

Another object of the instant invention is to provide a novel light source for use in forming the phosphor dot pattern in color tubes of the shadow-mask type, wherein the intensity of light rays impinge upon the regions of the tube face near the edges thereof are greatly enhanced in intensity.

These and other objects of the instant invention will become apparent when reading the accompanying description and drawings in which:

FIGURE 1 is an elevated sectional view of a prior art lighthouse apparatus employing a conventional light source.

FIGURE 2 is an elevational view of the light source apparatus of the instant invention.

FIGURE 2a is a crosssectional view of an ideal lens for use in the light source apparatus of FIGURE 2.

FIGURES 3m and 3b are cross-sectional views of the lens of FIGURE 2 employed in the arrangement of the instant invention.

FIGURE 4 shows a cross-sectional view of a preferred embodiment of the lens employed in the light source apparatus of FIGURE 2.

FIGURE 4w is a perspective view of the lens of FIG- URE 4.

FIGURES 5a and 5b show radiation patterns in the vertical and horizontal planes for the light source of FIGURE 1.

FIGURES 6a: and 6b show radiation patterns in the vertical and horizontal planes for the light source of the instant invention.

Refering now to the drawings, FIG. 1 shows a sectional view of a lighthouse apparatus 10 employed for the purpose of forming a phosphor dot pattern in the three primary colors upon the screen 13a of the shadow-mask tube face 13. The cylindrical wall 11 of the color tube is mounted upon the housing 12 of lighthouse apparatus 10. The cylindrical side wall 11 positions and supports the face plate screen 13 of the tube as well as the shadowmask structure 14, which is provided with a plurality of apertures 14a therethrough. As is well known in the prior art, the color tube portion, comprising the cylindrical side wall 11, the screen 13, and shadow-mask structure 14, is disassociated from the remainder of the color tube structure during the lighthouse operation.

The base or floor 12a of housing 12 supports a light source comprised of a housing 15, which is supported upon a turntable v16, mounted for rotation about shaft 17 for a reason to be more fully described. Within the housing is a lamp 18, which may be, for example, a mercury arc lamp designed to emit a high intensity light ray in opening a of housing 15. Opening 15a supports a tapered light conduit 19 enclosed within secondary housing 20 so that the extreme end portion 19a of the tapered conduit protrudes through an opening in secondary housing 20. The conduit consists of a material of high transparency to rays of the particular Wave lengths employed.

The light rays 21 from point light source 19 pass through a corrective system 22 positioned upon a supporting structure 23 having a substantially large opening 24. The corrective lens system 20 is provided for the purpose of deflecting the light rays in the manner shown by the upper light ray portions 21a to correct for the effects of radial misregister and dynamic conversion. These phenomena are covered in detail in copending application Ser. No. 472,169 filed July 15, 1965, entitled Lens System for Color Television Tubes by James Schwartz et al. and assigned to the assignee of the instant invention. The corrective lens system 22 lends no novelty to the light source of the instant invention and it is suflicient, therefore, to understand that the lens 22 functions to compensate for the effects of radial misregister and dynamic convergence phenomena which occur in shadow-mask color tubes. For a detailed description of such lens system reference should be made to the copending application referred to immediately above.

The light rays 21 emanating from point light source 19 in the region of the underside of corrective lens 22, have an intensity pattern which is substantially the configuration of a circle as represented by the phantom line curve 25. Thus light rays 21 which intersect line 25 will all have equal magnitudes of light intensity along any arc such as, for example, the arc 25 with the center of the are being the tip of point light source 1911. This radiation pattern being the case, it can clearly be seen that since the interior surface 13a of tube face 13 is relatively flat as compared to are 25, that light rays 2111 at the outer extreme face will be of significantly lower light intensity than the light rays striking in the central region of tube face 13a. This effect is increased when using a tube 90 or more deflection angle.

The turntable 16 upon which the light source is mounted can be seen to position the light source, which lies along line 1% at an eccentric angle relative to the axis 17a of the shaft 17. In addition thereto turntable 16 is provided with three slots 26 (only two of which are shown in FIG. 1) which are arranged at intervals around turntable 16. These slots 26 cooperate with a detent 27 which is spring loaded by device 28 for the purpose of locking turntable 16 into one of the three angular positions. This turntable arrangement is provided for the purpose of locating the tip 19a of point light source 19 at the effective color center of one of the three electron beams provided in the shadow-mask color tube. For example, in the phosphor dot formation process, the interior face 13a of the color tube is coated with a phosphor material of one of the three primary colors. The tube face and the shadow mask 13 and 14, respectively, are then positioned upon the lighthouse structure in the manner shown in FIG. 1, and the turntable is accurately located with the point light source occupying the same position as the electron beam occupies within the color tube for the particular phosphor material which has been deposited upon interior tube face 13a. The tube face 13 is then removed from the lighthouse apparatus and undergoes a washing operation in which all unexposed areas of the phosphor material are washed away from the tube face. During a second and third operation the tube interior face 13a is coated with the second and third remaining phosphor colors and the light source turntable 16 is rotated to move the point light source 1901 to the positions occupied by the second and third remaining electron beams so as to complete the phosphor dot formation process. The description "and mode of operation of the turntable 16 is set forth in detail in U.S. Patent No. 2,885,935, for example, and this turntable apparatus lends no novelty to the device of the instant invention.

The light source apparatus 30 of the instant invention is shown in FIG. 2 and may be substituted for the light source arrangement of the prior art shown in FIG. 1 by suitably being mounted upon turntable 16 or any other similar light source positioning apparatus. The light source 3% of the instant invention is comprised of a substantially dome-shaped reflector member 31 which has an ellipticalshaped reflective surface portion 32, which surface has been rotated downwardly about the prime focus point 41 for a purpose to be more fully described.

A mercury arc lamp 40 is positioned along the longitudinal axis 42 of the light source apparatus 30, with the illuminating mercury arc being positioned at the prime focal point 41. Suitable power source means (not shown) are connected to the electrodes 43 and 43a of lamp 40.

The upper housing portion 44 of the light source structure St} is secured to the reflector portion 3-1 by suitable fastening means 33 and is provided with an opening 50 for receiving the lens 45.

The mercury are located at prime focal point 41 of mercury arc lamp 40 emits light rays in substantially all directions. Considering the light rays reflected from the extreme edges of the reflective surface portion 32, it can be seen that the downward directed light ray 46 is reflected from the extreme lower point 32' of reflective surface 32, thereby assuming the light ray path 46a and striking a point lying on curve 45a in lens 45. The substantially circular shaped curve 45a which is the focus locus of all light rays reflected by the reflector 31 results from the fact that the mercury arc lamp 40 is not an ideal point light source and, therefore, light rays cannot focus at the ideal focal point 48 in lens 45. The assembly has therefore been designed to cause the light rays to focus on a locus curve 45a to compensate for imperfections in the light source. Considering the upper extreme edge 32" of reflector surface 32, it can be seen that light ray 49 emitted from the light source strikes the reflector surface at 32" and assumes the path 49a, striking the locus curve 450. In a like manner a light ray 51 impinging upon the intermediate region of reflect-or surface 32 is deflected and assumes path 51a. This light my also has its focal point along the locus curve 45a.

As is well known in the optics field, the amount of deflection which the light rays experience is a function of the angle of incidence of the light ray upon the entry surface, the index of refraction of the lens, and the angle of incidence which the light ray makes at the exit surface of the lens. The prime objective of the light source apparatus of the instant invention is to deflect the light rays in such a manner that the maximum number of light rays emitted from the light source will be emitted at no greater than a 45 angle, relative to the longitudinal axis 42, assuming the use of a 90 deflection ty-pe color tube.

Considering the lens configuration of FIG. 2a for the case in which the light source is an ideal point light source, the lens 45' shown in FIG. 2a has a curved entry surface 52 which closely approximates a pseudosphere or invert sphere. Entering light rays 55- are refracted by ideallens surface 52 so as to be emitted at the exit surface 53 at an angle of 45 relative to the light source longitudinal axis 42.

Since the light source, as a practical matter, is not an ideal point light source, this necessitates a modification in the configuration and design of the focusing lens, resulting in a lens 50 having the configuration shown in FIGS. 2 and 3a and 3b. In order to provide for a maximum number of light rays to be deflected at a maximum angle of 45 from the light source longitudinal axis 42 and selecting the lens material of fused quartz having an index of refraction n. equal to 1.48 for a wavelength of light equal to 3650 angstroms, it is desired to ascertain the angle which the entry surface 52 of lens 45 makes with the longitudinal axis 42.

We now cant or rotate the designed contour reflector 31 clockwise and counterclockwise about the prime focus point 41 as shown by arrows 31a and 31b. This produces a circular locus rather than a point locus. Assuming the locus curve 45a to be a circle of 4 diameter and assuming a maximum converging light intensity making an angle at 30 from the vertical axis 42, it is desired that the lens provide a deflection from 30 to 45 angle range from vertical axis 42 so as to bring the maximum number of light rays into focus at the exit surface.

Applying Snells Law, in order to determine the angle which the surface 52 makes with the longitudinal axis 42, wherein this angle is 0, we arrive at the equation:

sin 60n sin 45 Thus, it is found that the optimum entry surface forms an angle of l8- /z with the light source longitudinal axis 42. Having determined the optimum angle which the entry surface makes with the longitudinal axis 42, it is next desired to relate the design of the entry surface to the exit surface 56 (see FIG. 3a) so as to minimize the size of the outgoing bundle of light rays being emitted from the light source. Considering FIG. 30, for example, the objective is to locate the plane 56' of the exit surface 56 so that it intersects the smallest part or neck portion of the bundle of light rays 57. This may be done simply by plotting the light rays and selecting that portion of the bundle of light rays which is narrowest and this is a simple optical ray tracing problem.

It should be noted that the entry surface 52 of the lens 50 may be extended as shown by the dotted line 52 (see FIG. 4) so as to form a cone-shaped configuration. Employing a lens of this design, it is found that the amount of vertical light, i.e. light rays emitted from the exit surface parallel to longitudinal axis 42, will be substantially less than is the case of a truncated conical design wherein the bottom surface 52a is a flat surface as opposed to the bottom of the lens ending in a tip 58 (i.e. the apex of the cone).

The optimum position for the bottom surface 52a is determined by the position of the peripheral light ray 57'. Considering FIG. 2 it can be seen that the top enclosure portion 44 of the light source housing completely covers the top flat surface 58' of lens 45 so that the peripheral ray 57 which exits forming a 45 angle with the vertical or longitudinal axis 42, intersects the entry surface 55 at 59, thus establishing the optimum location for the bottom surface 57. The position of the bottom surface 57 may be altered to vary the ratio of light rays emitted at an angle of 45 relative to the light rays emitted which are parallel to the longitudinal axis 42. By moving the optimum surface 57, as shown in FIG. 3b, toward the right as shown by arrow 60, this increases the amount of vertical light emitted by the lens 50. By moving the bottom surface 57 in the direction shown by arrow 61 this, conversely, reduces the amount of vertical light emitted by lens 50.

Employing all of the design criteria set forth above, FIG. 4 shows the optimum lens design giving dimensions and angular relationships for all of the lens surfaces. FIG. 4a shows a perspective view of the resulting lens configuration of FIG. 4.

The advantages of the light source configuration of the instant invention can thus be appreciated from a consideration of FIGS. 5a and 5b, with FIGS. 6a and 6b, respectively. As shown in FIG. 5a considering the use of an ideal point light source 70, the radiation pattern for the light rays 71 is a circular pattern 72. Thus the intersection of all light rays 71 upon the circular curve 72 are equal in intensity. Taking a cross-sectional view of the radiation pattern 72 it can be seen that the light rays are on the directional as shown by the circle 73. Using the light source of the instant invention the radiation pattern is shown by the curve 74 which has a cardioidic shape. Assuming normalized intensity values, the vertical light ray 75 (i.e. an undeflected light ray) has an intensity value of 1.0. Light rays at the maximum deflection angle of 45 from the vertical axis have intensity values of 2.5. Thus it can be seen that light rays which will be directed toward the periphery-of the tube face shown in FIG. 1, is. light rays undergoing the maximum deflection from the vertical, have a greatly increased intensity value relative to the undefiected light rays 75, whereas compared with the ideal point light source shown in FIG. 5a, the light rays directed toward the edges of the tube face are at best equal in intensity to the undeflected light rays and, as a practical matter, are found to be substantially lower in intensity than the vertically-directed light ray 71'.

Considering the horizontal pattern of the cardioid curve 74, this curve 76' has a circular shape as does the curve 73 shown in FIG. 512 so that the light rays are on the directional in the horizontal plane.

It can therefore be seen from the foregoing description that the instant invention provides a novel light source configuration for use in shadow-mask color tube light house structures in which the light rays striking the tube face during the phosphor dot positioning process are greatly enhanced in intensity as compared with conventional methods.

Although I have described preferred embodiments of my novel invention, many variations and modifications will now be obvious to those skilled in the art, and I prefer therefore to be limited not by the specific disclosure herein but only by the appended claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. Apparatus for use in lighthouse structures employed for forming the phosphor dot pattern in shadow mask color tubes comprising a housing for supporting a tube 7 face and associated shadow mask, said apparatus being positioned within said housing and comprising:

a second housing having an opening;

a source of light within said second housing;

reflector means for deflecting light rays emitted from said light source toward said second housing opening;

a lens positioned within said second housing opening for deflecting light rays directed toward said opening toward said color tube face wherein the light rays directed toward the edges of said tube face are substantially greater in intensity than the light rays directed toward the central region of said tube face.

2. The apparatus of claim 1 wherein said source of light is a mercury arc lamp.

3. The apparatus of claim 1 wherein said lens has an entry surface having a truncated conical configuration.

4. The apparatus of claim 1 wherein said lens has an entry surface having a truncated conical configuration, and said exit surface has asecond conical configuration.

5. The apparatus of claim 4 wherein entry surface is contained substantially within said housing and said exit surface projects outwardly from said second housing through said opening.

6. The apparatus of claim 1 wherein said reflector means has a curved reflecting surface which is substantially elliptically shaped.

7. The apparatus of claim 1 wherein said reflector means has a curved reflecting surface which is substantially el-liptically shaped; said source of light being positioned substantially at the prime'focal point of the elliptically shaped curve.

3. The apparatus of claim 1 wherein said lens has an entry surface positioned within said second housing; and an exit surface projecting outwardly from said second housing through said opening; said exit surface being inclined at an angle to the longitudinal axis for said lens; said angle being selected to maximize the number of light rays emitted from said lens and directed toward the marginal edges of said tube face.

9. The apparatus of claim 8 wherein said exit surface is inclined at a second angle relative to said lens longitudinal axis; said angle being in the range from 41 to 49.

References Cited UNITED STATES PATENTS 2,817,276 12/1957 Epstein et al. 95-1 2,941,457 6/1960 Weingarten 951 2,942,099 6/1960 Goldstein 951 XR 3,211,067 10/1965 Kaplan 95-1 3,259,038 7/1966 Burdick et a1. 951

NORTON ANSHER, Primary Examiner.

R. M. SHEER, Assistant Examiner. 

